Ice detector



De; n), 1957.. 'KR-'EGE'RY 2,818,233 A l i ,cgntcmx mma Jan. 28; 1954 TRANSMISSION 2 3 WAVELENGH IN MLCRGNS WVENTOR v ALBERT F. KRUEGER ATTORNEY 251.6233. 0R IN1 ESQ/333.,

patented Desio, 1957 xcn cerramos.-.

itrueger, Needham, Mass., assigner to Elec.- Aironcs Corporation ,of America, a corporation of Massachusetts ApplcationJanuai-y 23, 1954, Serial No. 406,788 4 claims. (ci. 25o-sas) This invention relates to ice detectors. Under certain atmospheric conditions, 'a coating of ice can form very vrapidly on the surface of aircraft, jamming controls and, v

in the case' of jets, obstructing the air-intake ducts. It is therefore important that the formation of ice be de. tected rapidly in order to act-uatc the tie-icing apparatus with which aircraft are equipped.

`1t is, therefore, an object of this invention to provide an icc detector the response of which is very rapid.

lt isl another object of this invention to provide an ice detector which is simple and economical to build. f In accordance with the illustrated embodiment of the l (present invention, use is made of the `absorption characteristcs of ice, which is practically opaque to infrared radiation having a wave length greater than 1.3 microns. A source of radiant energy containing infrared radiafi tion directs a beam onto a photoelectric cell sensitive to @infrared radiation. A filter which greatly attcnuates t radiation having a wave length less than 1.3 microns is 'i positioned between the source `of radiant energy and the lphotoelectric cell. `With this filter alone interposed beitween the source and the photoelectric ccll, infrared radiation having a wave length greater than 1.3 microns `impingcs upon the photoolectric cell. When ice is also ginterposed between the source and the photoelcctric cell, ,infrared radiation having a wave length greater than t 1.3 microns is greatly attenuated, and no radiation im- .pinges upon the photoelectric cell. A lcontrol circuit lwhich is responsive to this change of radiant energy impinging upon the photoelectric cell actuates the deicing apparatus.

i ,f Other and incidental obie'cts of the present invention x.

will be apparent to those skilled in the art from a reading (of thc following specificationl and an inspection of the accompanying drawings in which;

Figure 1 shows by means of a graph the near infrared r transmission characteristics of ice and of a `filter suitable for use in the icc detector of the present invention;

Figure 2 illustrates diagrammatically la proposed arrangement of the ice detector to protect the air-intake ducts of ajet aircraft; and

yFigure 3 is a circuit diagram of an embodiment of the ice detector iu accordance with the present invention.

Referring to Figure 1, the curve 11 ,shows the transmission characteristics of ice in the near infrared region of the spectrum. It can -le seen that ice absorbs radiation having a wave ,length greater than 1.3 microns and passes radiation having a. wave length less than 1.3 microns. Curve i3` shows the transmission characteristics of a Corning No. 5113 filter which is practically opaque to radiation having a wave length less than 1.3 microns or greater than 3.3 microns. 4

Figure 2 i1. a cross-sectional view of the nose of a jet aircraft. Air ducts are provided between the outs-ide walls 15 of the fuselage and the inner cone 17. When theA aircraft is in motion, air ntshes in the direction of arrows 19 toward the engine compartment. The air usually goes through a screen (not shown) to prevent stones and other soiid objects from damaging the engine. The ice Ldetector is so installed that it supervises a critical area of" the aircraft, i. e., an area where ice formation usually starts. The screen and the tip of the. inner cone 17 are examples of such critical areas, and Figure 2 shows an arrangement which supervises ice formation at the tip of the inner cone 17. A source of infrared radiation, such asian incandescent lamp 21, emits a beam 22 which is focused through a lens system 23 onto a photoelectric cell. 25. -A Corning No. 5113 filter 27 intercepts the beam 22 before it reaches the photoelectric cell 25.

With the filter 27 interposed -between the light source 21 and the photocell 2S, infrared radiation lying in the range from 1.3 to. 3.3 .microns impinges upon the photocell 25. When ice 29 intercepts the beam 22, by formiug at the tip of the inner core 17 or on thc walls 15,

radiation above 1.3 microns is absorbed by the ice and prevented from impinging upon the photocell 25 which is therefore in the dark."

'Figure 3 shows u suitable control circuit to actuate the dcr-icing apparatus 31. The photoelectric cell 25 is a lead sulfide photoconductive cell and is'connected in abridge circuit comprising the -cell 25, resistor 33, and the two sections and 37 of a potentiometer having a tap 39. A battery 40 is connected across' terminals 41 and 43 of the bridge. An electron valve or tube 4S has its cathode 47 connected to the junction lg Aof photocell 25 and resistor 33, its control grid 51 connected to tap 39, and its anode 5 3 connected through a relay'SS tothe power supply terminal 57.

The operation of the control circuit of Figure 3 is as follows: with no ice in the path of the beam 22, radiant energy impinges upon the photocell 25, the resistance of which is therefore lowered. The potential at junction .point 49 has a given negative value with respect to ground, and thepotential atv the control grid 51, which is also negative, is adjusted -by means of tap 39 so that tube does not conduct. When radiant energy is prevented'from impinging upon the photon-.11,25 -by the formation of i'ce 29 in the path of the bea'nll, the r2- sistance of photocell 25 is increased, `and the poten-tial junction point 43 becomes more negative This reduces the bias on tube 45 which becomes conductive. Conduction through tube l5 closes the rela-y 55 which actuales thc de-icin`Y apparatus 31.

Iclaim;

l. An ice detector comprising: a source of radiation,

.a radiation-'sensitive device, and a filter positioned between said source and said rndiationsensitive device, said filter attenuating wave lengths passed by ice and passing wavelengths absorbed by ice. y A 2. An ice detector comprising: a source of infrared radiation, photoelectric .means sensitive to said infrared radiation, and filter means positioned between said source and said photoelectric means, said filter means attenuating, infrared radiation having wavewlengths below 1.3 microns.

3. An ice detector comprising: a source of infrared radiation over a band including wave lengths passed by ice and wave lengths absoi'bed by ice, photoelectric means sensitive to infrared radiation within said band, and filter means positioned between said source and said photoelectric means, said filter means passing the wave lengths absorbed by ice and attenuating the wave lengths passed by ice.

enteras radiation, and her means` positioned between said sourc and said photoeiectric means, saidviter means attendaiting radiation wiihin saidband which is passed by ice.

a sou'rce of radiation,'

Rcferenccs Cited invlhe file of this patent UNITED STATES PATENTS Mobsby Apr. i, Eastman v Mar. 1G, McDermott Dec; 3, Friedman et al. Sept. 6,

Blom et al. Oct. 10, 

